1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition and, more particularly, to a radiation-sensitive resin composition suitable as a chemically-amplified resist useful for microfabrication utilizing various types of radiation, for example, deep ultraviolet rays such as a KrF excimer laser or ArF excimer laser, X-rays such as synchrotron radiation, or charged particle rays such as electron beams.
2. Description of the Background Art
In the field of microfabrication represented by fabrication of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in order to achieve a higher degree of integration.
A conventional lithographic process utilizes near ultraviolet rays such as an i-line radiation. It is known in the art that microfabrication with a line width of sub-quarter micron using near ultraviolet rays is very difficult.
Therefore, use of radiation with a shorter wavelength has been studied for enabling microfabrication with a line width of 0.20 μm or less. Deep ultraviolet rays represented by a line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given as radiation with a shorter wavelength. Of these, a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (wavelength: 193 nm) have attracted attention.
As a resist applicable to the excimer laser radiation, a number of resists utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a component generating an acid (hereinafter referred to as “photoacid generator”) which generates an acid upon irradiation (hereinafter referred to as “exposure”) has been proposed. Such a resist is hereinafter called a chemically-amplified resist.
As such a chemically-amplified resist, Japanese Patent Publication No. 27660/1990 discloses a resist comprising a polymer containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. The t-butyl ester group or t-butyl carbonate group in the polymer dissociates by the action of an acid generated upon exposure, whereby the polymer has an acidic group such as a carboxylic group or a phenolic hydroxyl group. As a result, exposed areas of the resist film become readily soluble in an alkaline developer.
Most of conventional chemically-amplified resists use a phenol resin as a base resin. Deep ultraviolet rays used as radiation for exposure are absorbed due to an aromatic ring in the resin and cannot sufficiently reach the lower layers of the resist film. Because of this, the dose of the radiation is greater in the upper layers and is smaller in the lower layers of the resist film. This causes a resist pattern to be slimmer in the upper portion but broader toward the lower portion, thereby forming a trapezoid shape after development. No sufficient resolution can be obtained from such a resist film. Such a trapezoid resist pattern formed after development cannot give a desirable dimensional accuracy in the succeeding steps such as an etching step and an ion implantation step. In addition, if the configuration of the upper resist pattern is not rectangular, the resist disappears faster during dry etching, making it difficult to control etching conditions.
The shape of the resist pattern can be improved by increasing the radiation transmittance through the resist film. For example, (meth)acrylate resins represented by polymethylmethacrylate are desirable from the viewpoint of radiation transmittance due to superior transparency to deep ultraviolet rays. Japanese Patent Application Laid-open No. 226461/1992 proposes a chemically-amplified resist using a methacrylate resin, for example. However, in spite of the excellent micro-processing performance, this composition exhibits only poor dry etching resistance due to the absence of an aromatic ring, giving rise to difficulty in performing etching with high accuracy. This composition thus does not have both radiation transmittance and dry etching resistance at the same time.
As a means to improve dry etching resistance of the chemically-amplified resist without impairing the radiation transmittance, a method for introducing aliphatic rings into the resin component of the resist instead of aromatic rings has been known. For example, Japanese Patent Application Laid-open No. 234511/1995 discloses a chemically-amplified resist using a (meth)acrylate resin having aliphatic rings.
This resist includes groups which comparatively easily dissociate by conventional acids (acetal functional groups such as tetrahydropyranyl group, for example) and groups which are comparatively difficult to dissociate by acids (t-butyl functional groups such as t-butyl ester group or t-butylcarbonate group, for example) as acid-dissociable functional groups in the resin component. The resin component having the former acid-dissociable functional groups exhibits excellent basic characteristics as a resist, in particular, superior sensitivity and excellent pattern shape, but has poor storage stability as the composition. The resin component having the latter acid-dissociable functional groups has excellent storage stability, but exhibits impaired resist characteristics such as sensitivity and pattern shape. Moreover, inclusion of aliphatic rings in the resin component of this resist results in poor adhesion to substrates due to the extreme increase in hydrophobicity of the resin.
When forming a resist pattern using a chemically amplified resist, the resist is usually heated after exposure to accelerate dissociation of the acid-dissociable group. In this instance, if the heating temperature fluctuates, the resist pattern line width also fluctuates inevitably to a certain extent. However, to satisfy the requirement for microfabrication of integrated circuit elements in recent years, development of a resist exhibiting a small line width fluctuation according the heating temperature after exposure, i.e. exhibiting small temperature dependency, has been desired.
In addition, the photoacid generator is known to greatly affect the functions of a chemically-amplified resist. Presently, onium salt compounds which generate an acid upon exposure at a high quantum yield and exhibit high sensitivity are widely used as a photoacid generator for chemically-amplified resists.
As such onium salt compounds, triphenylsulfonium trifluoromethane sulfonate, triphenylsulfonium hexafluoroantimonite, triphenylsulfonium naphthalenesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, and the like are used. Most of these conventional onium salt compounds, however, do not exhibit satisfactory sensitivity. Although some compounds may exhibit comparatively high sensitivity, they are not necessarily satisfactory in overall resist performance such as resolution, pattern configuration, and the like.
In view of development of technology capable of dealing with recent progress in microfabrication of integrated circuit devices, a chemically-amplified resist which is applicable to short wavelength radiation represented by deep ultraviolet rays, exhibits high radiation transmittance, and excels in basic characteristics as a resist such as sensitivity, resolution, dry etching resistance, and pattern shape has been strongly demanded.
An object of the present invention is to provide a radiation-sensitive resin composition useful as a chemically amplified resist having high transmittance of radiation and exhibiting superior basic properties as a resist such as high sensitivity, resolution, dry etching tolerance, and pattern shape.